Log levels (TRACE, DEBUG, INFO, WARN, ERROR) in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to log an informational message using Spring Boot's Logger.

Spring Boot

logger.[1]("Application started successfully.");

Drag options to blanks, or click blank then click option'

Atrace

Binfo

Cerror

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using error or warn for normal info messages.

The info level is used for general informational messages that highlight the progress of the application.

2fill in blank

medium

Complete the code to log a warning message about low disk space.

Spring Boot

logger.[1]("Disk space is running low.");

Drag options to blanks, or click blank then click option'

Adebug

Binfo

Ctrace

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using info or debug instead of warn for warnings.

The warn level is used to indicate a potential problem or important situation that should be noticed.

3fill in blank

hard

Fix the error in the code to log a detailed trace message.

Spring Boot

logger.[1]("Entering method processData with parameters.");

Drag options to blanks, or click blank then click option'

Ainfo

Bdebug

Ctrace

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using debug instead of trace for very detailed logs.

The trace level is the most detailed and is used for very fine-grained debugging information.

4fill in blank

hard

Fill both blanks to log an error message with an exception.

Spring Boot

logger.[1]("Failed to save data.", [2]);

Drag options to blanks, or click blank then click option'

Aerror

Bwarn

Cexception

Dex

Attempts:

3 left

💡 Hint

Common Mistakes

Using warn instead of error for exceptions.

Passing wrong variable name for exception.

The error level is used for serious issues. The exception object is passed as the second argument to log the stack trace.

5fill in blank

hard

Fill all three blanks to create a debug log that shows the user ID and action performed.

Spring Boot

logger.[1]("User [2] performed [3] action.");

Drag options to blanks, or click blank then click option'

Adebug

B{}

Clogin

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using info instead of debug for detailed logs.

Not using placeholders for variables.

The debug level is used for detailed information useful during development. The placeholders {} are used to insert variables in the log message. Here, the action is 'login'.

Practice

1. Which log level in Spring Boot shows the most detailed information, typically used for diagnosing problems during development?

easy

A. ERROR

B. INFO

C. WARN

D. TRACE

Solution

1. Step 1: Understand log level hierarchy

   TRACE is the most detailed log level, showing fine-grained events.

2. Step 2: Compare with other levels

   INFO, WARN, and ERROR show less detail and focus on general info or problems.

3. Final Answer:

   TRACE -> Option D

4. Quick Check:

   Most detailed log = TRACE [OK]

Hint: TRACE logs show the tiniest details for debugging [OK]

Common Mistakes:

• Confusing INFO with TRACE as most detailed
• Thinking ERROR shows all details
• Assuming WARN is more detailed than DEBUG

2. Which of the following is the correct way to set the log level to WARN in application.properties for Spring Boot?

easy

A. logging.level.root=WARN

B. log.level=WARN

C. logging.level=WARN

D. logging.root.level=warn

Solution

1. Step 1: Recall Spring Boot logging property format

   The correct property is logging.level.root to set root log level.

2. Step 2: Check option syntax

   logging.level.root=WARN uses correct key and uppercase level, matching Spring Boot conventions.

3. Final Answer:

   logging.level.root=WARN -> Option A

4. Quick Check:

   Correct property key = logging.level.root [OK]

Hint: Use logging.level.root=LEVEL to set global log level [OK]

Common Mistakes:

• Using log.level instead of logging.level.root
• Incorrect property key like logging.root.level
• Using lowercase level names incorrectly

3. Given this Spring Boot code snippet:

logger.debug("Debug message");
logger.info("Info message");
logger.error("Error message");

If the log level is set to INFO, which messages will appear in the logs?

medium

A. Info message, Error message

B. Only Error message

C. Debug message, Info message, Error message

D. Only Debug message

Solution

1. Step 1: Understand log level filtering

   Setting level to INFO shows logs at INFO and higher severity (WARN, ERROR).

2. Step 2: Check which messages qualify

   DEBUG is lower than INFO, so it is hidden; INFO and ERROR show.

3. Final Answer:

   Info message, Error message -> Option A

4. Quick Check:

   INFO level shows INFO and ERROR logs [OK]

Hint: Logs show messages at set level and above [OK]

Common Mistakes:

• Assuming DEBUG logs show at INFO level
• Thinking ERROR logs are hidden at INFO level
• Confusing INFO with DEBUG level

4. You set logging.level.com.example=DEBUG in application.properties, but DEBUG messages from com.example.service do not appear. What is the most likely cause?

medium

A. DEBUG level is not supported in Spring Boot

B. The root log level is set higher than DEBUG, blocking DEBUG logs

C. The package name is misspelled in the property

D. You must restart the application to apply log level changes

Solution

1. Step 1: Check property correctness

   If the package name is misspelled, the setting won't apply to the intended classes.

2. Step 2: Evaluate other options

   DEBUG is supported; root level does not block specific package settings; restart is usually required but not the main cause.

3. Final Answer:

   The package name is misspelled in the property -> Option C

4. Quick Check:

   Correct package name is critical for log level settings [OK]

Hint: Check package spelling carefully in logging properties [OK]

Common Mistakes:

• Assuming root level overrides package level always
• Believing DEBUG is unsupported
• Ignoring typos in package names

5. You want to see detailed logs only for the com.example.repository package but keep the rest of the application logging at WARN level. Which application.properties configuration achieves this?

hard

A. logging.level.root=TRACE
logging.level.com.example.repository=WARN

B. logging.level.root=WARN
logging.level.com.example.repository=TRACE

C. logging.level.root=INFO
logging.level.com.example.repository=ERROR

D. logging.level.root=DEBUG
logging.level.com.example.repository=INFO

Solution

1. Step 1: Set global log level to WARN

   Set logging.level.root=WARN to limit logs globally to warnings and errors.

2. Step 2: Override package log level to TRACE

   Set logging.level.com.example.repository=TRACE to get detailed logs only for that package.

3. Final Answer:

   logging.level.root=WARN logging.level.com.example.repository=TRACE -> Option B

4. Quick Check:

   Global WARN + package TRACE = detailed logs only there [OK]

Hint: Set root level high, override package level low for details [OK]

Common Mistakes:

• Setting root level too low, flooding logs
• Overriding package with higher level than root
• Confusing package and root property keys